1. Field of the Invention
This invention relates to a cage for a stationary type constant-velocity joint (CVJ) comprising an outer ring and an inner ring, balls through which torque is transmitted between the outer and inner rings, and a cage for retaining the balls, and a method of manufacturing the cage, and a constant-velocity joint.
2. Description of the Related Art
FIG. 5 shows a conventional stationary type CVJ, which comprises an outer ring 50 formed with a plurality of curved track grooves 54 in its spherical inner surface 51, an inner ring 52 formed with a plurality of curved track grooves 55 in its spherical outer surface 53, radially opposite to the respective track grooves 54, and balls 56 each received in a pair of radially opposed track grooves 54 and 55.
The balls 56 are retained in pockets 60 of a cage 57 disposed between the inner and outer rings 52, 50 with its outer spherical surface 58 guided by the inner spherical surface 51 of the outer ring 50 and its inner spherical surface 59 guided by the outer spherical surface 53 of the inner ring 52.
The bottoms of the track grooves 54 and 55 are curved such that their respective centers of curvature Al and A2 are spaced (or offset) equal distances from point O0 in opposite directions along the axis of the rings. When torque is transmitted with the outer ring 50 and the inner ring 52 taking a working angle, the balls 56 are always in a plane perpendicular to the bisector of the working angle, so that the output ring can always rotate at a constant speed irrespective of the working angle.
The pockets 60 of the cage 57 are elongated in the circumferential direction of the cage as shown in FIG. 6A so that the balls 56 move in the circumferential direction in the pockets while sliding along the axially opposed side faces 61 as shown in FIG. 6B when the inner and outer rings are rotating with their axes inclined relative to each other. High wear resistance is therefore required for the side faces 61.
To increase the wear resistance of the side edges 61, a conventional CVJ cage 57 is manufactured following the next seven steps as shown in FIG. 7:
Step 1: forming a short tubular member P1 as shown at (A) by cutting a pipe;
Step 2: pressing the member P1 from both ends to form a cage blank P2 having outer and inner curved surfaces;
Step 3: turning the outer and inner surfaces into spherical outer and inner surfaces 58, 59 (C);
Step 4: pressing the cage blank P2 to form pockets 60 (D);
Step 5: shaving the perimeter of each pocket 60 to cut a pair of side faces 61 until the width between the side faces 61 becomes substantially equal to the diameter of the balls 56 (E);
Step 6: subjecting the cage blank P2 to heat treatment such as carburizing to increase surface hardness; and
Step 7: grinding the cage blank P2 (F) to finish spherical outer and inner surfaces 58, 59 to form a cage 57.
Because the cage blank is carburized after the pockets 60 have been formed, hardened layers 63 formed around the pockets 60 will have a uniform depth as shown in FIGS. 6A, 6B. The side faces 61 as the ball rolling surfaces have a pretty high hardness of 58-63 HRC. The cage 57 is thus sufficiently wear resistant.
When torque is transmitted with the inner and outer rings forming a working angle, tensile and torsional forces act on the cage 57. Thus, it is desirable to decrease the hardness to increase the toughness of the bridge portions 64 defined between the pockets 60.
But since the cage blank is carburized after the pockets have been formed and their side faces 61 have been finished by shaving, the hardened layers formed around the pockets 60 have a uniform depth as shown in FIG. 6B. The bridges 64 are thus high in hardness and low in toughness. Since the bridges 64 are formed by punching the pockets 60, they naturally have a trapezoidal cross-section, which means that their width (circumferential dimension) at their inner side is smaller than at their outer side. Thus, if the number of balls and thus the number of pockets are increased to increase the load-bearing capacity of the joint without increasing its outer diameter, the width of the bridge portion on the radially inner side tends to be short.
Therefore there are several points to be improved to increase the strength of such a conventional cage.
Also, with such a conventional cage 57, since the axially opposed side faces 61 of each cage 60 are finished by shaving, the width of the pockets 60 (or distances between the side faces 61) tends to vary rather widely.
Thus, in assembling a constant-velocity joint, it is necessary to classify the cages 57 into ranks according to the width of the pockets 60, classify the torque-transmitting balls into ranks according to the respective pocket widths, and adjust the gaps between the pockets 60 and the torque-transmitting balls 56. If no suitable gaps are obtainable, there arises a necessity of grinding the side faces 61 of the pockets 60. Thus, assembling is extremely troublesome and there remain points to be improved.
An object of the invention is to provide a cage for a constant-velocity joint that is high in mechanical strength, and a method of manufacturing such a cage, and a durable constant-velocity joint.
According to this invention, there is provided a cage of a stationary type constant-velocity joint having an outer ring and an inner ring. The cage has a cylindrical portion formed with a plurality of pockets at equal angular intervals to receive balls for transmitting a turning torque between the outer ring and the inner ring. The cage has a spherical outer surface kept in contact with and guided by a spherical inner surface of the outer ring and a spherical inner surface kept in contact with and guided by a spherical outer surface of the inner ring. The pockets each have a pair of end faces that are opposed to each other in a circumferential direction of the cage and a pair of side faces that are opposed to each other in an axial direction of the cage. Also, the pair of end faces are formed by cutting after hardening and have a lower surface hardness than the side faces.
The center of curvature of the spherical outer surface of the cylindrical portion may beat the same point as or spaced from the center of curvature of its spherical inner surface in an axial direction of the cylindrical portion.
By this arrangement, toughness is imparted to the bridge portions formed between the pockets and their tensile and torsional strengths are improved.
As a method for providing a lower surface hardness to a pair of the end faces of each pocket than a pair of the side faces, either of the following two methods may be adopted. One is to form the cylindrical portion of the cage with pockets from carburized case-hardened steel and cut the entire inner periphery of each pocket with the cutting depth deeper to form a smaller carburizing depth on the end faces than on the side faces, and the other is to cut only the end faces, thereby forming a smaller carburizing depth on the end faces than on the side faces.
The end faces of the pockets may be cut to inclined surfaces that incline so as to diverge radially outwardly.
On the constant-velocity joint comprising an outer ring, an inner ring and a cage mounted between the outer ring and the inner ring so that the center of curvature of the spherical outer surface of the cage is axially spaced from the center of curvature of the spherical inner surface of the cage, when torque is transmitted with the outer ring and the inner ring taking a working angle therebetween, the balls received in the pockets of the cage move along a path forming a figure xe2x80x9c8xe2x80x9d which is larger at its radially outer half than at its radially inner half. By forming the end faces of each pocket into inclined surfaces that incline so as to diverge radially outwardly, the width of each bridge portion at its inner side is increased. This increases the strength of the bridge portions.
According to this invention, there is also provided a method of manufacturing a cage of a constant-velocity joint comprising the steps of turning outer and inner surfaces of a tubular cage blank to form spherical outer and inner surfaces, pressing the cage blank to form a plurality of pockets at equal angular intervals, hardening the cage blank by carburizing, grinding the spherical outer and inner surfaces of the cage blank after heat treatment, and cutting a pair of end faces of each of the pockets so that the pair of end faces will have a lower surface hardness than a pair of side faces of the pockets.
By adopting such a method, a cage is provided which has bridge portions having toughness and which has a high mechanical strength.
According to this invention, there is also provided a stationary constant-velocity joint comprising an outer ring, an inner ring, the outer ring being formed with a plurality of curved track grooves in a spherical inner surface thereof and the inner ring being formed with a plurality of curved track grooves in a spherical outer surface thereof. The center of curvature of the track grooves of the outer ring and the center of curvature of the track grooves of the inner ring are offset by equal distances in opposite directions from the angular center of the joint. Torque-transmitting balls are mounted between the track grooves formed in the outer ring and the track grooves formed in the inner ring. Also included is a cage having a cylindrical portion formed with a plurality of pockets at equal angular intervals to receive the balls for transmitting a turning torque between the outer ring and the inner ring. The invention is characterized in that the pockets each have a pair of end faces that oppose each other in a circumferential direction of the cage and a pair of side faces that oppose each other in an axial direction of the cage, and the pair of end faces are formed by cutting after hardening and have a lower surface hardness than the pair of side faces.